Shock absorbing underlayment for artificial playing surfaces

ABSTRACT

The present invention is directed to an underlayment composition for an artificial playing surface comprised of a butadiene rubber, such as polybutadiene or styrene-butadiene that is commercially available as recycled polycord tires that have been granulized. An inorganic-base moisture-retaining agent such as vermiculite or perlite is also included in the composition in addition to a binder comprised of a mixture of isocyanate polyurethane and an inorganic acid. The present invention also provides a method of making the present composition. The method comprises the steps of mixing thoroughly granulized particles of butadiene rubber in a mixing container, mixing an inorganic-based moisture-retaining component with the butadiene rubber, mixing an acid having a pH ≦3 with the butadiene rubber and the inorganic-based moisture-retaining component, and mixing an isocyanate polyurethane with the butadiene rubber, the inorganic-based moisture-retaining component and the acid. Finally, the present invention also provides a method of using the present composition which comprises the steps of applying the composition over a conventional foundation base and laying an artificial turf over the underlayment composition.

This application is a division of Ser. No. 08/289,764, filed on Aug. 12,1994, now U.S. Pat. No. 5,514,722, and entitled "Shock AbsorbingUnderlayment for Artificial Playing Surfaces," currently pending, whichis commonly assigned with the present invention and is incorporatedherein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention is directed to an underlayment for artificialplaying surfaces, and more particularly is directed to an underlaymenthaving moisture retaining and high shock-absorbing capabilities.

BACKGROUND OF THE INVENTION

Games and various sports activities have been a part of civilization formost of recorded time and have, in fact, grown dramatically inpopularity in the United States and around the world over the lastcentury. Many types of playing surfaces have been developed to provide asuitable surface on which to conduct these various sports activities.

One of the first of such playing surfaces was a natural grass surface.Grass fields offer several advantages for conducting different types ofgames and related activities. For instance, natural grass fields providean excellent shock-absorbing cushion for athletes as they run, jump anddive their way to victory over their opponents. This is an importantaspect of any playing surface, since it is well known that the athlete'sbones, joints and body, in general, absorb a great deal of shock forcewhen impacting the playing surface while performing various athleticmaneuvers. Maximum absorption of shock forces helps to reduce injuriesthat may arise when the athlete's body is subjected to shock forces overtime.

Another advantage grass fields offer is that they provide excellenttraction in dry weather conditions, allowing the athlete to keep properbalance and thereby more properly execute athletic maneuvers.

A further advantage grass fields offer is that they contain moisture intheir grass root systems. The moisture functions in two ways. First, themoisture acts as a natural heat dissipator that, in turn, provide arelatively cool surface on which to perform the physically demandingactivities. Second, the moisture functions as a lubricant to provides anappropriate amount of friction co-efficient reduction to prevent"footlock"--a situation that arises when the athlete's shoe momentarilysticks or drags on the turf, sometimes causing the athlete to stumble orfall. This second function also helps to prevent immediate injuries,because, when the athlete is hit by another player, the moisture in thegrass surface allows the athlete's foot to slide across the surfaceinstead of sticking to the surface. This lubricating action greatlyreduces the chance of injury to the legs, and particularly to the kneesor ankles. Additionally, natural grass fields absorb and drain water toan acceptable degree.

To this point, the discussion has been directed primarily toapplications of grass fields in playing sports such as baseball,football, soccer or other outdoors sports that require a playing field.In addition to these applications, however, grass turf is alsoapplicable in a golf course setting. The reason is that the variousgrass turfs customarily found on golf courses offer an ideal playingsurface. For instance, the moisture content of the greens gives theright amount of ball stopping control as a ball is hit onto the green.Also, putting is affected by the amount of moisture available in theturf. Additionally, the impact absorption capability is a significantfactor in properly stopping an in-flight ball on the green. While grassfields and turfs have several advantages and applications, there are,unfortunately, certain disadvantages associated with grass fields andturf.

One such disadvantage is that grass fields, of course, become very muddyand slippery when exposed to large amounts of water in a short period oftime and, when excessively wet, they can be torn up rather quickly.Another disadvantage is that many of today's sports arenas are domed andenclosed for year round comfort of the spectators and the athletesalike. As such, natural grass fields are less desirable in theseenclosed areas because of inadequate exposure to sunlight. Still anotherdisadvantage is that grass fields require constant watering, fertilizingand general maintenance to keep them in an ideal playing condition. Thisupkeep is very expensive in that it requires substantial amounts of timeand money for maintenance crews and supplies.

With respect to applications involving golf courses, the natural grassturf also has the same disadvantages regarding upkeep and generalmaintenance with even more cost and time involved. For example, teeboxes undergo regular abuse as successive golfers make divots in thesurface of the turf while teeing-off from the box. The boxes, therefore,require constant replacement of sod and turf and, in some cases, requirethe provision of more than one tee box for each hole. Another example isthe damage that occurs to greens when the balls impact the green and thephysical damage that is often done by golfers and harsh weatherconditions. Finally, grass and especially green grass can be verysusceptible to frost damage, fungus and various other types ofenvironmental conditions.

Another type of artificial turf that has been extensively used over thelast two decades is "ASTRO TURF®", which is comprised of strands ofextruded plastic. The "ASTRO TURF®" is laid over a shock absorbingunderlayment and a foundational hard base. Other types of artificialturfs include loop-pile carpet-like turfs, knitted nylon orpolypropylene turfs or polypropylene tufted turfs.

The foundational hard base conventionally consists of a stone materialthat may vary in depth, depending on the intended use. The hard base isnormally formed by depositing the stone material in a layer of at leastsix inches deep to a tolerance of plus or minus one inch and sloped in apredetermined direction for water drainage. The layer is then compacted,watered for optimum moisture content, and rolled to a compaction rate of95% standard procter density. The compacted stone material is thennormally oiled with a primer of hot, liquid asphalt to seal the materialand provide bonding for subsequent deposition of an asphalt layer ontop. Next, hot-mix asphalt is laid in place by conventional pavingequipment. On top of this asphalt is laid a conventional underlayment orshock pad over which the artificial turf is laid.

Conventional underlayment shock pads typically consist of a hardenedmixture of rubber granules and either a polyurethane, polyethylene orpolyvinyl chloride binder in combination with a small pebble or stoneapproximately 4 to 9 mm in diameter. The conventional mixture forms whatis known as a "closed cell" system, where multitudes of noncontiguousair pockets are trapped in the mixture. These pads average 5/8 inches inthickness when laid over the hard base asphalt. While the combination ofthe artificial turf and the underlying shock pad overcome some of thedisadvantages associated with the natural grass field or turf, theyintroduce, however, several other disadvantages.

One such disadvantage is that many of the conventional shock pads areclosed-cell systems. Again, a closed cell system is one in which thecells within the pad structure are not interconnected with one anotheror the surface of the pad. As such, the pad cannot "breathe", i.e, waterand air cannot move into and out of the pad. In fact, the typicalclosed-cell system pad is specifically designed to repel moisture toenhance the water shedding capabilities of the playing surface ingeneral. Thus, the pad neither retains moisture nor allows moisture topass therethrough. This is a significant disadvantage because there isno moisture present to act as a natural lubricant, thereby preventingfootlock, or to act as a natural heat dissipator, thereby providing acooler playing surface.

Another disadvantage of the closed-cell system is that the closed-cellpads collapse over time, increasing the shock to the athlete, in turntransmitting greater shock to the athlete's body upon impact.Furthermore, the pads are initially limited in shock absorption,especially from greater heights, which, of course, increases the amountof force that the athlete's body absorbs when it impacts the surface.

Still another disadvantage of the prior art shock pads is that they usea polyurethane foam that causes the pad to be too rigid and hard. Thisrigidity and hardness detracts further still from the pad's ability toabsorb the appropriate amount of impact shock. In addition, pebbles orstones are usually incorporated making the pad even harder still andthus even less capable of absorbing the appropriate amount of impactshock.

While some open-celled systems do exist, they also suffer fromdisadvantages. For example, as with closed-celled systems, open-celledsystems typically include pebbles or stones and polyurethane foams inthe mixture. As previously stated, polyurethane foams cause the pad tobecome hard and less absorbent over time. In addition, moisture cannotbe entrained or entrapped within the pad because the pads are typicallydesigned to allow water to pass through them to drain water effectivelyfrom the playing surface. Thus, footlock and a high playing fieldtemperature are also prevalent in these conventional open-celled systemsas well.

Applications of the conventional underlayments discussed above withrespect to golf courses are unsatisfactory for basically the samereasons. First, the base or shock pad does not contain enough moistureto effectively simulate a natural grass green regarding its ability tostop an in-flight ball landing on the green. Moreover, the pad lacks therequired degree of energy absorption that is necessary to properly stopthe ball and that is necessary for absorbing the impact of the golf clubas the golfer hits the tee shot from the tee box.

Accordingly, what is needed in the art is a shock absorbing underlaymentthat is durable, absorbs shock in the manner of a natural grass fieldand retains moisture to lubricate the surface of the artificial turf toprevent footlock and provide a playing surface that is cooler. The shockpad of the present invention addresses these needs.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, it is aprimary object of the present invention to provide an underlayment thatis durable and that in combination with an overlaying turf has thedesirable qualities of natural grass. In the attainment of theabove-described primary object, the present invention provides in ashock absorbing underlayment composition comprising a butadiene rubberthat comprises from about 90% to about 85% by weight of the composition,an inorganic based moisture-retaining component that comprises fromabout 3% to about 1% by weight of the composition, and a binder mixtureobtained by mixing an isocyanate polyurethane that comprises from about10% to about 8% by weight of the composition and an acid that comprisesfrom about 1.6% to about 0.2% of the composition wherein the mixturecomprises from about 12% to about 8% by weight of the composition.Preferably the butadiene rubber comprises from about 88% to about 86% byweight of the composition, and more preferably comprises about 86% byweight of the composition.

In another aspect of the preferred embodiment, the butadiene rubber isselected from the group consisting of polybutadiene rubber andstyrene-butadiene rubber. Preferably, the butadiene rubber is comprisedof granulized polycord tires having a shore A ranging from about 40 toabout 70 with the granules preferably range in size from about 6millimeters to about 2 millimeters in diameter and with the polycordselected from the group consisting of nylon and polyester. Morepreferably, however, the shore ranges from about 45 to about 65 and mostpreferably ranges from about 50 to about 60.

The inorganic-based moisture-retaining component of the presentcomposition preferably comprises from about 2% to about 1% by weight ofthe composition and in a more preferred embodiment, the inorganic-basedmoisture-retaining component comprises about 2% by weight of thecomposition. The inorganic-based moisture-retaining component isselected preferably from the group consisting of hydrated aluminumsilicate and volcanic glass. The hydrated aluminum silicate ispreferably vermiculite and the volcanic glass is preferably perlite.

The binder mixture preferably comprises from about 12% to about 9% byweight of the composition and more preferably comprises about 12% byweight of the composition. The isocyanate polyurethane component of thebinder mixture is preferably a methylene di-p-phenylene isocyanatepolyurethane while the acid is preferably an inorganic acid selectedfrom the group consisting of sulfuric, nitric, hydrochloric andphosphoric. More preferably, the inorganic acid is an acid mixture of a20% concentration by weight of sulfuric acid and a 20% concentration byweight of hydrochloric acid in an aqueous medium, wherein the acidmixture has a pH ≦ 3.

The various components of the present composition combine to form anunderlayment that preferably has an open-celled structure and a shockabsorbency factor from a drop height of 24 inches ranging from about 85gs to about 90 gs, a shock absorbency factor from a drop height of 36inches ranging from about 120 gs to about 125 gs, a shock absorbencyfactor from a drop height of 48 inches ranging from about 180 gs toabout 200 gs, and a shock absorbency factor from a drop height of 96inches ranging from about 275 gs. to about 300 gs.

In another aspect of the present invention, in a preferred embodimentthereof, there is provided a process for making a shock absorbingunderlayment composition comprising the steps of: a) mixing thoroughlygranulized particles of butadiene rubber in a mixing container with thebutadiene rubber comprising from about 90% to about 85% by weight of thecomposition, b) mixing an inorganic-based moisture-retaining componentwith the butadiene rubber with the inorganic-based moisture-retainingcomponent comprising from about 3% to About 1% by weight of thecomposition, c) mixing an acid having a pH ≦ 3 with the butadiene rubberand the inorganic-based moisture-retaining component with the acidcomprising from about 1.6% to about 0.2% by weight of the composition,and d) mixing a isocyanate polyurethane with the butadiene rubber, theinorganic-based moisture-retaining component and the acid with theisocyanate polyurethane comprising from about 10% to about 8% by weightof the composition, with the underlayment preferably having anopen-celled structure.

Preferably, the butadiene rubber is selected from the group consistingof polybutadiene rubber and styrene-butadiene rubber and is comprised ofgranulized polycord tires having a shore A ranging from about 40 toabout 70, and more preferably having a shore A ranging from about 50 toabout 65. The polycord is preferably selected from the group consistingof nylon and polyester and the polycord tires are granulized to a sizeranging from about 6 millimeters to about 2 millimeters in diameter.

The inorganic-based moisture-retaining component is preferably selectedfrom the group consisting of hydrated aluminum silicate and volcanicglass. The hydrated aluminum silicate is preferably vermiculite and thevolcanic glass is preferably perlite.

The isocyanate polyurethane of the present composition is preferably amethylene di-p-phenylene isocyanate polyurethane while the acid ispreferably an inorganic acid selected from the group consisting ofsulfuric, nitric, hydrochloric and phosphoric. More preferably, theinorganic acid is an acid mixture of a 20% concentration by weight ofsulfuric acid and a 20% concentration of hydrochloric acid in an aqueousmedium.

In yet another aspect of the present invention, there is provided amethod of using the shock absorbing underlayment composition comprisingthe steps of: a) making the composition in a mixing container with thecomposition comprising: butadiene rubber comprising from about 90% toabout 85% by weight of the composition, an inorganic-basedmoisture-retaining component comprising from about 3% to about 1% byweight of the composition, and a binder mixture obtained by mixing aisocyanate polyurethane comprising from about 10% to about 8% by weightof the composition and an acid comprising from about 1.6% to about 0.2%of the composition wherein the mixture comprises from about 12% to about8% by weight of the composition with the composition having anopen-celled structure, thereby allowing water to substantially draintherethrough, b) uniformly applying the composition to a foundationalsubstrate surface in a thickness ranging from about 19 mm to about 102mm and c) trowelling the composition to a substantially level, smoothfinished surface.

The butadiene rubber is preferably comprised of granulized polycord tirehaving a shore A ranging from about 40 to about 70 and having a sizeranging from about 6 millimeters to about 2 millimeters in diameter, thebutadiene rubber selected from the group consisting of polybutadienerubber and sytrene-butadiene rubber. The inorganic-basedmoisture-retaining component is preferably selected from the groupconsisting of vermiculite and perlite. The isocyanate polyurethane ispreferably methylene di-p-phenylene isocyanate polyurethane while theacid is an inorganic acid mixture of 20% concentration by weight ofsulfuric acid and 20% concentration of hydrochloric acid in an aqueousmedium having a pH ≦ 3.

In another aspect of the present invention, the method of using furthercomprises the steps of forming a foundational substrate surface, thesteps comprising: a). uniformly forming a compacted sub-grade base layerhaving a minimum thickness of about 154 mm, b). uniformly forming acompacted substantially level intermediate layer over the sub-grade baselayer having a minimum thickness ranging from about 26 mm to about 38mm, and uniformly laying a first porous pad over the intermediate layer.The sub-grade base layer may be formed from stone sub-base material. Thestep of forming the sub-grade base may also include positioning drainpipe in the sub-grade base and sculpting the sub-grade base to drainwater to the drain pipe and applying a first porous pad over thesub-grade base material.

In yet another aspect of the method of using, the method may furthercomprise the steps of uniformly applying hot liquid asphalt over thestone sub-base material and uniformly applying a hot-mix asphalt as theintermediate layer over the stone sub-base material. In yet anotherembodiment, the intermediate layer may be comprised of a stone material.A second porous pad may be applied over the intermediate layer if sodesired.

The method using may also include the step of uniformly laying anartificial turf over the composition surface where the artificial turfmay be an extruded plastic fiber turf, a knitted nylon, a knittedpolypropylene or a tufted polypropylene.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention so that the detailed description ofthe invention that follows may be better understood. Additional featuresand advantages of the invention will be described hereinafter which formthe subject of the claims of the invention. Those skilled in the artshould appreciate that they can readily use the disclosed conception andspecific embodiment as a basis for designing or modifying otherstructures for carrying out the same purposes of the present invention.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the inventionas set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a cross-sectional view of an artificial playingsurface system with a drainage system placed therein;

FIG. 2 illustrates a cross-sectional view of a another artificialplaying surface system;

FIG. 3 illustrates a graph of impact curves for different prior artunderlayments as compared to natural grass and the present underlaymentcomposition; and

FIG. 4 illustrates a graph of impact curves for various underlaymentformulations as compared to natural grass and the present underlaymentcomposition.

DETAILED DESCRIPTION

The underlayment composition of the present invention provides a uniqueshock absorbing, moisture-retaining underlayment that provides manyadvantages commonly associated with natural grass turf. The presentcomposition permits air and moisture to enter and exit the underlayment,which provides for both grass-like traction and a cooler playingsurface. At the same time, however, the underlayment permits substantialamounts of water to drain through the pad, thereby allowing properdrainage to occur. Additionally, the present composition provides anopen-celled structure that has the desired degree of soft-hardness ratioand resiliency to adequately absorb shock in a more efficient mannerthan conventional underlayments. These characteristics make theunderlayment well suited for artificial playing surfaces, such as "ASTROTURF®" and other carpeted playing surfaces, especially where grass-likeshock absorbance, traction and general playing conditions are desired.

In the broadest scope, the underlayment composition of the presentinvention is comprised of synthetic rubber, an inorganic-basedmoisture-retaining component and a binder mixture obtained by mixing anisocyanate polyurethane and an acid. This unique combination yields anunderlayment with several unexpected results as discussed in detail,below.

In a preferred embodiment, the synthetic rubber may be a butadienerubber comprising from about 90% to about 85% by weight of thecomposition. More preferably, the butadiene rubber is polybutadiene orstyrene-butadiene rubber that preferably comprises from about 88% toabout 86% by weight of the composition. Most preferably, however, thebutadiene rubber is a styrene-butadiene that comprises about 86% byweight of the composition. The synthetic rubber is preferably granulizedwith the granules having a diameter that allows for maximum sized airvoids while giving the desired degree of softness-hardness and strength.Preferably, the granules' size range from about 6 millimeters to about 2millimeters in diameter. A preferable source for the granulizedsynthetic rubber is recycled tires that are commercially available fromnumerous sources, such as American Recycled Tires, Midland, Mich.; TLJ,Inc., St. Louis, Mo.; W & W Recycling Rubber, Saugus, Mass. and TireIncorporated, Charlotte, N.C. The granulized rubber is preferablycomprised of granulized reinforced polycord tires with no steel presentand with the polycord being comprised of nylon or polyester.

To provide an underlayment with the desirable amount of shock absorbencyand traction, it is preferred that the synthetic rubber have a certaindegree of softness-hardness and resiliency. To that end, it ispreferable that the recycled tires have a shore "A" of about 40 to about70 as measured by the American Standard Test and Measurements ("ASTM")scale for tire hardness, ASTM No. D2240-68. This shore gives thegranulized rubber the desired amount of softness-hardness and resiliencyrequired in most applications. More preferably, however, the tires havea shore A of about 45 to about 65, and most preferably, have a shore Aof about 50 to about 60. Of course, it will be appreciated that theshore may range several units higher or lower than the range juststated, depending on the performance requirements desired for theunderlayment surface as applied to various applications.

The inorganic-based moisture-retaining agent gives the underlaymentcomposition important properties that set it apart from conventionalunderlayments. For instance, typical underlayments do not usemoisture-retaining agents because the conventional thought with respectto artificial playing surfaces has been that water hinders traction andshould be removed. Thus, reflected in the prior art has been an emphasisto purposefully design the underlayment to shed as much water aspossible. As a result, conventional underlayments cannot simulatenatural grass because they lack the essential amount of moisture. Asstated in the Background, moisture is a necessary component to preventfootlock and provide a cooler playing surface.

In contrast, however, the underlayment composition of the presentinvention includes an inorganic-based moisture-retaining agent, whichallows it to retain moisture. As used herein, the term"moisture-retaining agent" means an agent that can both retain andrelease moisture or water. In other words, the moisture or water doesnot become permanently entrapped within the composition, but is allowedto evaporate and be replaced. Thus, the moisture-retaining agent in theunderlayment composition, in effect, reduces the co-efficient offriction by acting as a moisture reservoir continuously releasingmoisture to the overlaying artificial turf, thereby reducing potentiallyinjuring footlock. Additionally, the moisture-retaining agent acts as ancooling agent by the process of heat dissipation through waterevaporation to provide a cooler playing surface. As such, theunderlayment of the present invention closely simulates preferrednatural grass-like conditions.

The inorganic-based moisture-retaining agent of the present invention ispreferably a hydrated aluminum silicate, including organopolysilicates,or volcanic glass and comprises from about 3% to about 1% by weight ofthe composition and more preferably comprises from about 2% to about 1%by weight of the composition. The hydrated aluminum silicate ispreferably a three-layered phyllosilicate comprised of a trioctahedralwith brucite-type layers or a dioctahedral with gibbsite-type layershaving water retention and releasing properties. More preferably,however, the hydrated aluminum silicate is vermiculite ormontmorillonite. The volcanic glass is preferably acommercially-available processed perlite that has been heated untilexpanded to a frothy product. The effects of the presence of theinorganic-based moisture agent are reflected in TABLE II, below and arediscussed below in more detail in the Experimental Results section.

The next component of the present composition invention is a mixtureobtained by mixing an isocyanate polyurethane and an acid. Preferablythe isocyanate polyurethane comprises from about 10% to about 8% byweight of the composition and more preferably from about 9% to about 10%by weight of the composition. The isocyanate polyurethane is preferablya methylene di-p-phenylene isocyanate polyurethane that is a pigmentedliquid with a boiling point of 392° F., an evaporation rate less than 1(butyl ether=1), a vapor density greater than 1 (air=1), and a specificgravity of 1.10. An example of an isocyanate polyurethane that iscommercially available is "FUTURA-TECH 8805", Product No. 08805500manufactured by Futura Coatings, Inc., 9200 Latty Ave., Hazelwood, Mo.63042 in which a polyisocyanate comprises from about 79% to about 95% byweight of the polyurethane composition that has a vapor pressure of lessthan 0.1 mm Hg at 25° C. and a vapor density of 8.6 and a cyclic esterthat comprises from about 0% to about 8% by weight of the polyurethanecomposition.

The isocyanate polyurethane is mixed with an acid, preferably in themanner as described below. The acid preferably comprises from about 0.2%to about 1.6% by weight of the underlayment composition and morepreferably comprises from about 0.2% to about 1.0% by weight of thecomposition. The acid is preferably an inorganic acid selected from thegroup of hydrochloric acid, sulfuric acid, nitric acid or phosphoricacid, and more preferably, is an aqueous mixture of equal amounts of 20%concentrated by weight hydrochloric acid and 20% concentrated by weightsulfuric acid having a pH ≦3. The combination of the isocyanatepolyurethane and the acid foams the polyurethane and reduces standrigidity and reduces the polyurethanes natural stiffness. It is believedthat the reaction of the various components adds tremendous amounts ofair entrainment to the polyurethane (up to 28% air voids) and forms anopen-celled structure within the underlayment, which adds shockabsorbency. Thus, the combination yields the unexpected result of anunderlayment having a polyurethane component that is less rigid and moreresilient than conventional formulations, thereby causing theunderlayment to have a greater shock absorbing capacity thanconventional formulations. The shock absorbency advantages offered bythe unique present invention are discussed and illustrated below in moredetail in the Experimental Results section.

A preferred embodiment of the present composition is made in thefollowing manner:

Place approximately 100 pounds of recycled granulized nylon or polyestercord tire rubber with the granules ranging in size from about 6 mm toabout 2 mm in diameter into an empty paddle mixer container while themixer is running. The rubber granules should be mixed thoroughly forabout two to three minutes or until the rubber is thoroughly broken intothe individual granules. With the mixer still running, add approximately1 pound each of commercially processed, dry vermiculite and perlite tothe granulized rubber and mix the dry components until thoroughly mixed.To the dry mixture, add a total of 6 fluid ounces of an aqueous mixturecomprised of equal volumetric amounts of 20% concentrated by weighthydrochloric acid and 20% concentrated by weight sulfuric acid as themixture is continuously stirred. Next, slowly add approximately 13.75pounds of polyisocyanate polyurethane on top of the rolling, or mixingcomposition, so as not to saturate any one area excessively. Then, mixthe total mixture for no less than three minutes before emptying themixer.

Normally, all materials are mixed thoroughly after the three minute timeperiod. However, the operator should visually inspect the rolling mix todetermine if the composition is thoroughly mixed after the three minuteperiod. The mixture is then emptied from the container and spread on thefoundational substrate. The mixture may be hand screeded by conventionalmethods onto the foundational surface or the mixture may be screeded bya conventional mechanical spreader. In either case, it is important toachieve a uniformly and substantially level surface having no divots,trowel marks, valleys or holes. What is meant by "substantially level"is that the surface may be uniformly slanted a few degrees, as isconventionally done, to achieve proper drainage from the playingsurface. After the underlayment is trowelled to a smooth finish, theunderlayment material is compressed to approximately twelve pounds persquare foot. Of course, in applications involving golf courses, theunderlayment and the foundational layers would be sculpted to conform tothe desire topographical contours of the golf course.

As previously stated, the underlayment composition of the presentinvention is exceptionally well suited for applications directed toartificial playing surfaces such as football fields. Turning now to FIG.1, there is illustrated a cross-sectional view of a playing surfaceutilizing the underlayment composition of the present invention as itrelates primarily to new field or area construction having adrain-through system incorporated therein. A normal sub-grade 10 iscompacted to 95% standard procter density and is sculpted to drain to adrainage channels 12 on twenty-five foot centers or as localgeographical conditions demand. In the center of the drainage channels12 is a perforated four, six, or eight inch diameter drain pipe 14extending to header drains, not shown. The size of the pipe is dictatedby the size of the area, as well as yearly rainfall totals in thelocale. Laid over the sub-grade 10 is preferably a non-woven geotextilepad 16 or membrane known as a soil separator. Pad 16 allows water topercolate through it to the drainage channels 12 and keeps the basestone material 18 from washing into the drain lines and reducing thedrainage flow. The non-woven geotextile is preferably made from recycledplastic bottles extruded into tiny fibers for the body of the fabric.The base stone material 18 is laid over the sub-grade material 10 andthe pad 16 and compacted to 95% standard procter density. The thicknessof the base course may vary from one geographical locale to another. Asecond non-woven geotextile pad 20 is uniformly laid over the base stonematerial 18 and is used as a soil separator and also used to separatethe base stone materials from the shock absorbing underlayment 22. Theweight of the second pad 20 is preferably in the range of between twelveand thirty ounces. The second pad 20 will actually be the backing thatgives additional horizontal strength to the shock absorbing underlayment22. The shock absorbing underlayment 22 is uniformly laid over thesecond pad 20 and the base stone material 18 in the manner previouslydescribed above to a preferable thickness ranging from about 25 mm toabout 102 mm. It should be understood, however, that the thickness mayvary beyond the stated ranges, depending on the use requirements of theunderlayment. An artificial turf 24 is then uniformly laid over theshock absorbing underlayment. The artificial turf may be anyconventional artificial surface covering, such as an extruded plastic"ASTRO TURF®" covering or knitted nylon or polypropylene or tuftedpolypropylene.

Turning now to FIG. 2, there is illustrated a cross-sectional view of amore conventional artificial surface and foundational base structureutilizing the underlayment composition of the present invention. A stonesub-base material 26 is initially laid down over a prepared foundationalbase, not shown. The sub-base 26 is normally a minimum of six inches indepth and shaped to a tolerance of plus or minus one inch and sloped ina direction a minimum of 0.83% or more. The sub-base 26 is thencompacted, watered for optimum moisture content, and rolled to acompaction rate of 95% standard procter density. Next, the sub-base 26is oiled with a primer of hot, liquid asphalt, similar to MC-30, forsealing and bonding. Next, a hot-mix asphalt layer 28 is laid in placeby paving equipment to a thickness of at least 25 mm to 39 mm inthickness. However, this depth also may vary in different geographicallocales. A non-woven geotextile pad 30 is laid over the asphalt layer 28and a shock absorbing underlayment 32 of the present invention is thenuniformly laid over the pad 30 at a thickness ranging from about 19 mmto about 102 mm. Again, it should be understood, however, that thethickness may vary beyond these stated ranges, depending on the userequirements of the underlayment. The pad 30 allows water to percolatethrough the underlayment 32 and drain off the field between the asphaltlayer 28 and the pad 30. An artificial turf 34 is then uniformly laidover the underlayment 32.

EXPERIMENTAL RESULTS

Impact measurements were taken for two different prior art formulationsalong with the present invention underlayment composition and comparedwith impact measurements taken on natural grass turf. The impactreadings were taken with a drop testing unit called a "G-MAX" unit, andthe impact forces were measured in gs. The results of these readings areillustrated in FIG. 3, which is a graph of the impact curves fordifferent turf underlayment types with the y-axis representingacceleration, measured in gs and the x-axis representing the drop heighttaken at 24 inches, 36 inches, 48 inches and 96 inches. Two measurementswere taken for each turf type and the range between the two readings isrepresented by the hatched-in area in FIG. 3. The results illustrated inFIG. 3 are a comparison of grass, designated #1 the present composition,designated #2, Prior Art "B", which is a rubber-stone,polyurethane-based system, designated #3 and Prior Art "A", which is apolyvinyl chloride-based closed-cell system, designated #4.

As seen from FIG. 3, the present composition more closely simulates theshock absorbency of natural grass, particularly at a drop height rangingfrom 24 inches to 48 inches and is only 100 gs higher at the height of96 inches. In stark contrast, however, the prior art underlaymentcompositions show a substantially higher impact force from the same dropheight than the present composition. Thus, it is seen from FIG. 3 thatthe underlayment of the present composition has shock absorbencyproperties that are far superior to the prior art formulations and moreclosely simulates the shock absorbency of natural grass.

Two different impact measurements were also taken for differentformulations, including a prior art formulation and the underlaymentcomposition of the present invention and compared with impactmeasurements taken for natural grass turf. The impact readings weretaken with same drop testing unit note above. The averages of theseresults are shown in TABLE I and graphically illustrated in FIG. 4, withthe y-axis representing acceleration, measured in gs and the x-axisrepresenting the drop height taken at 24 inches, 36 inches, 48 inchesand 96 inches.

                  TABLE I                                                         ______________________________________                                            FORCE IN                                                                      gs          24 inches                                                                              36 inches                                                                            48 inches                                                                            96 inches                              ______________________________________                                        1.  GRASS       80       100    150    200                                    2.  10%    Pu       87.5   122.5  190    287.5                                    6 oz.  acid                                                                   2%     vermic.                                                                88%    SBR                                                                3.  6%     PU       135    250    365    475                                      14%    stone                                                                  80%    SBR                                                                4.  10%    PU       132.5  200    325    425                                      0%     acid                                                                   0%     vermic.                                                                90%    SBR                                                                5.  7%     PU       102.5  115    185    275                                      0%     acid                                                                   0%     vermic.                                                                93%    SBR                                                                6.  12%    Pu       150    285    385    500                                      0%     acid                                                                   0%     vermic.                                                                88%    SBR                                                                ______________________________________                                    

The results of TABLE I as illustrated in FIG. 4 are a comparison ofgrass, designated #1, the present composition, designated #2, Prior Artformulation comprised of 6% polyurethane ("PU"), 14% stone and 80%styrene-butadiene rubber ("SBR"), designated #3, a first contrastingformulation comprised of 10% polyurethane, 0% acid, 0% vermiculite and90% styrene-butadiene rubber, designated #4, a second contrastingformulation comprised of 7% polyurethane, 0% acid, 0% vermiculite and93% styrenebutadiene rubber, designated #5 and a third contrastingformulation comprising 12% polyurethane, 0% acid, 0% vermiculite and 88%styrene-butadiene rubber, designated #6.

As seen from TABLE I and FIG. 4, there is a distinct contrast betweenthe forces absorbed between the composition of the present invention andthe prior art and contrasting formulas. The only exception isformulation #5, which somewhat parallels the results obtained for thepresent composition. However, this formulation is not acceptable because(1) the material easily unravels and (2) it is too soft, possibly givingrise to injury by an athlete catching his foot on the playing surface.Furthermore, this particular formulation lacks the essentialmoisture-retaining agent, vermiculite. The other formulations, includingthe prior art clearly show that the composition of the present inventionhas far superior shock absorbing impact properties.

In addition to the impact tests that were conducted, moisture retentiontests were also conducted on two different prior art formulations andthe present invention underlayment composition as compared to themoisture capabilities of natural grass. The following results are basedon a comparison of grass, the present composition (PC), Prior Art "A",which is a polyvinyl chloride-based closed-cell system without amoisture-retaining agent and Prior Art "B", which is a rubber-stone,polyurethane-based system without a moisture-retaining agent. Thecomparison was based on a 2 inch rainfall/hour at a temperature of 80degrees and a controlled humidity of 50%. The results of this comparisonare reported in TABLE II, below.

                  TABLE II                                                        ______________________________________                                                                   PRIOR ART                                                                              PRIOR ART                                 CONDITIONS                                                                              GRASS    PC      "A"      "B"                                       ______________________________________                                        Dry Weight                                                                              125 lbs. 60 lbs. 8 lbs.   63 lbs.                                   Sample                                                                        1 sq. yd.                                                                     Moisture  75%      25%     0%       4%                                        Retention                                                                     After 1 hr.                                                                   Moisture  22%      10%     0%       0%                                        Retention                                                                     After 24 hrs.                                                                 Air Voids for                                                                           25%      30%     0%       20%                                       Breathable Base                                                               ______________________________________                                    

As seen from TABLE II, after a period of 24 hours, the underlayment ofthe present invention still has a 10% moisture retention whereas thePrior Art "A" and "B" formulations have 0% moisture retention. Thus, inaddition to the superior shock absorbency, the underlayment of thepresent invention has superior moisture retention capabilities ascompared to the prior art formulations. Furthermore, the underlayment ofthe present invention more closely simulates the moisture retention ofnatural grass.

The results reflected by TABLE I also show that air voids within anunderlayment do not have any effect on its ability to retain moisture.For example, even though Prior Art "B" has 20% air voids, it still doesnot retain any moisture after a 24 hour period.

From the above description, it is apparent that the present inventionprovides an underlayment that provides both excellent shock absorbencyand moisture retention properties.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims.

What is claimed is:
 1. A method of using a shock absorbing underlaymentcomposition, said method comprising the steps of:(a) making saidcomposition in a mixing container, said composition comprising:fromabout 90% to about 85% by weight of butadiene rubber, based on theweight of said composition; from about 3% to about 1% by weight of amoisture-retaining component selected from the group consisting ofhydrated aluminum silicate, organopolysilicate and volcanic glass basedon the weight of said composition; and from about 12% to about 8% byweight of a binder mixture, based on the weight of said composition,said binder mixture comprising from about 10% to about 8% by weight ofan isocyanate polyurethane, based on the weight of said composition andfrom about 1.6% to about 0.2% by weight of an acid, based on the weightof said composition; (b) uniformly applying said composition to afoundational substrate surface in a thickness ranging from about 19 mmto about 102 mm; and (c) trowelling said composition to a substantiallylevel, smooth finished surface.
 2. The method of claim 1 wherein saidbutadiene rubber is comprised of granulized polycord tire having a shore"A" ranging from about 40 to about 70 and having a size ranging fromabout 6 millimeters to about 2 millimeters in diameter, said butadienerubber selected from the group consisting of polybutadiene rubber andstyrene-butadiene rubber.
 3. The method of claim 1 wherein saidisocyanate polyurethane is methylene di-p-phenylene isocyanatepolyurethane.
 4. The method of claim 1 wherein said acid is an inorganicacid mixture of 20% concentration by weight of sulfuric acid and 20%concentration by weight of hydrochloric acid in an aqueous medium havinga pH ≦3.
 5. The method of claim 1 further comprising the steps offorming a foundational substrate surface, said steps comprising:a)uniformly forming a compacted sub-grade base layer having a minimumthickness of about 154 mm; b) uniformly forming a compactedsubstantially level intermediate layer over said sub-grade base layerhaving a minimum thickness ranging from about 26 mm to about 38 mm; andc) uniformly laying a first porous pad over said intermediate layer. 6.The method of claim 5 wherein said compacted sub-grade base layer isformed from a stone sub-base material.
 7. The method of claim 6 furthercomprising the steps of uniformly applying hot liquid asphalt over saidstone sub-base material and uniformly applying a hot-mix asphalt as anintermediate layer over said stone sub-base material.
 8. The method ofclaim 7 further comprising the step of uniformly laying a second porouspad over said intermediate layer.
 9. The method of claim 7 wherein saidintermediate layer is comprised of a stone material.
 10. The method ofclaim 5 wherein said step of forming said compacted sub-grade baseincludes positioning drain pipe in said compacted sub-grade base andsculpting said compacted sub-grade base to drain water to said drainpipe.
 11. The method of claim 1 further comprising the step of uniformlylaying an artificial turf over said composition surface.
 12. The methodof claim 11 wherein said artificial turf is an extruded plastic fiberturf.
 13. The method of claim 11 wherein said artificial turf is aknitted nylon.
 14. The method of claim 11 wherein said artificial turfis a knitted polypropylene.
 15. The method of claim 11 wherein saidartificial turf is a tufted polypropylene.
 16. The method of claim 1wherein said composition has an open-celled structure allowing water tosubstantially drain therethrough.
 17. A method of using a shockabsorbing underlayment composition, said method comprising the stepsof:(a) making said composition in a mixing container, said compositioncomprising:from about 90% to about 85% by weight of butadiene rubber,based on the weight of said composition; from about 3% to about 1% byweight of a moisture-retaining component selected from the groupconsisting of vermiculite and perlite based on the weight of saidcomposition; and from about 12% to about 8% by weight of a bindermixture, based on the weight of said composition, said binder mixturecomprising from about 10% to about 8% by weight of an isocyanatepolyurethane, based on the weight of said composition and from about1.6% to about 0.2% by weight of an acid, based on the weight of saidcomposition; (b) uniformly applying said composition to a foundationalsubstrate surface in a thickness ranging from about 19 mm to about 102mm; and (c) trowelling said composition to a substantially level, smoothfinished surface.